carbohydrate chemistry for medical students

1. Dr.S.Sethupathy,M.D.,Ph.D.,
Division of Biochemistry,
Rajah Muthiah Medical College,
Annamalai University

2.  Carbohydrates are polyhydroxy
aldehydes (-CHO) or
ketones(-C-CO-C-) or
compounds that yield them on
hydrolysis.
 Glucose- aldohexose
 Fructose-ketohexose

4.  Ring structure represents Hemi acetal form
which is the condensation of an aldehyde or
keto with a hydroxyl group.
 Glucose exists as a six membered pyranose
ring.
 Fructose exists as five membered furanose
ring structure.

8.  Compounds having same structural formula
but different spatial configuration and it is
due to asymmetric carbon atom.
 Asymmetric carbon (Chiral carbon ) means
four different groups are attached to that
carbon.
 The possible stereoisomers depend on the
number of asymmetric carbons
 The formula 2n where n is the number of
asymmetric carbons present in the molecule.

10.  Due to the presence of asymmetric carbon,
when plane polarized light is passed through
the sugar solution, it will be either rotated to
right or left.
 If it is rotated to right, it is called
dextrorotatory (+) and if to left, it is
levorotatory(-).
 Racemic mixtures contain equal amounts of
(+) and (-) isomers and so NO rotation .

11.  Enantiomers are chiral molecules that are
mirror images of one another. An example of
an enantiomer is the D and L isomers of
glucose.
 Diastereomers are stereoisomers are not
mirror images of one another and are non-
superimposable on one another.
Stereoisomers with two or more stereocenters
can be diastereomers. Eg: D-Glucose and D-
Altrose.

12.  Epimers: Another type of isomer ,
carbohydrates can take on are epimers.
 Epimers are diastereomers that differ in
configuration of only one stereogenic center.
ie : two diastereomers that differ only at one
stereocenter.

14.  When a monosaccharide gets cyclized from
chain structure , its carbon 1 becomes
asymmetric and forms α and β anomers.
 Eg α ,D-Glucose and β D-glucose.
 If hydroxyl group is below the plane of the
ring, it is α , D-glucose and if it is above, it is
β anomer.

16.  Mutarotation : It is the change in the specific
optical rotation due to inter conversion of α,
β anomers.
 α ,D-glucose – +α112 0 – β ,D glucose +
190 At equilibrium + 52.5 0 when α and β
anomers will be in the ratio of approximately
1:2.

18.  Sugars due to their free aldehyde or keto group
reduce cupric ions into cuprous ions and give red
precipitate.
 Sucrose is non reducing sugar due to absence of
free aldehyde or keto group.
 Starch is also a non reducing sugar due to
insufficient number of reducing groups.
 Molish test is the general test for carbohydrates.
Sugars when treated with concentrated .sulfuric
acid, they get dehydrated to form furfural
derivatives which on condensation with phenolic
compounds give colored products.

19.  All reducing sugars will form osazone with
excess of phenyl hydrazine on boiling.
 Osazones are insoluble and different sugars
give characteristic form of crystals. Because it
involves Carbon 1 and 2 of glucose, fructose
and mannose form needle shaped crystals as
the difference is masked.
 Maltaosazone will give sunflower shaped
crystals and lactosazone will give hedge-hog
shaped or badminton ball shaped crystals.

21.  Sugar acids: Glucose on mild oxidation by
Bromine water, the aldehyde group is
oxidized to form aldonic acid.
 In system, aldehyde group is protected and
the last hydroxyl group is oxidized to form
glucuronic acid.
 Under strong oxidation, both aldehyde and
last hydroxyl groups are oxidized to form
dicarboxylic saccharic acids.

23.  On reduction of aldehyde group of glucose , it
forms sorbitol.
 In diabetes mellitus, sorbitol accumulates in the
lens causing early cataract.
 Fructose on reduction can form both sorbitol
and mannitol.
 Mannose can form mannitol.
 Mannitol is an osmotic diuretic and used to
reduce intracranial tension.
 Galactose can form galactitol or dulcitol and its
accumulation in the lens causes early
development of cataract in galactosemia
condition.

25.  Hydroxyl groups of sugars (Usually the
second carbon of hexoses) are substituted
with amino group to give amino sugars.
 Amino sugars do not show reducing property
and do not form osazones also.
 Glucosamine is present in hyaluronic acid,
heparin and blood group substances.
 Galactosamine is present in chondroitin
sulfate of cartilage , bone and tendons.
 Mannosamine is present in glycoproteins.

26.  Removal of oxygen from hydroxyl group
results in the formation of deoxy sugar.
 2-Deoxy ribose is formed by removal of
oxygen from hydroxyl of second carbon in
ribose
 It is the sugar present in Deoxy ribo nucleic
acid (DNA) .
 Feulgen staining using Schiff’s reagent is
specific for 2-Deoxy ribose (DNA) in tissues.

27.  Ribose is present in RNA ,ATP ,NAD and 2-
deoxy ribose is present in DNA.
 Ribulose is an intermediate in HMP shunt
pathway.
 Xylulose is an intermediate in uronic acid
pathway.

29.  Monosaccharides
 Further cannot be broken in to simpler sugars
 Eg: glucose, ribose, fructose, xylulose
 Oligosaccharides- 2- 10 monosccharides on
hydrolysis
 2- disaccharides
 Maltose- glucose + glucose
 Lactose- glucose + galactose
 Sucrose- glucose + fructose

30.  Homopolysccharides – single type of
monosccharides- Starch, glycogen,
cellulose- glucose
 Heteropolysaccharides- more than one type
of monosaccharides
 Heparin. Chondroitin SO4, dermatan SO4,
Hyaluronic acid- Mucopolysccharides

31.  It is cane sugar. It is a non reducing sugar
 Aldehyde glucose and keto group of fructose are
involved in the linkage and are not free to reduce the
Benedict’s reagent.
 But its hydolysate products reduce the reagent.
 Hydrolysis of sucrose : The products of hydrolysis
have reducing property.
 The optical rotation of sucrose is +66.5 and after
hydrolysis it changes to – 39. This change is called
inversion and is due to the fact that on hydrolysis, it
yields glucose (+52.5 ) and fructose (- 92) which is
greater than glucose.
 The hydrolysate is called invert sugar and is sweeter
than sucrose. Honey contains invert sugar.

35.  Maltose is composed of two glucose
molecules linked by alpha-1,4linkage. It is a
reducing disaccharide. It forms sunflower
shaped osazone crystals.
 Isomaltose is composed of two glucose
molecules linked by alpha-1,6 linkage.
 Intestinal enzyme isomaltase hydrolyzes
isomaltose. It is a reducing sugar.

36.  Starch is of plant origin, composed of
amylase and amylopectin.
 Amylose is unbranched and contains only
α1,4 linkage. Amylopectin has both α -1, 4
and α -1, 6 linkages.
 Starch forms blue colored complex with
iodine. It is non reducing .
 Amylase enzyme acts on starch and finally
hydrolyzes them to maltose and isomaltose.

38.  Inulin is a polyfructosan in beta-1,2 linkage
and it is used for Renal Glomerular
filtration rate assessment .
 Cellulose contains β 1, 4 linkage and so it is
not acted upon by amylase .
 It is hydrolyzed by cellulase enzyme. It is
absent in human digestive system. So it is
indigestible and forms roughage in the feces.

40.  Dextrans are branched homoglycans of
glucose units with α 1,4, α 1,6, α 1, 3
linkages , produced by microorganism
 It is used as plasma volume expander to treat
hypovolemic shock.

41.  It is composed of (beta 1,4 linkage)D-
glucuronic acid and (beta -1,3 linkage) N-
acetyl-D-glucosamine repeating units.
 It does not contain sulfate.
 It is present in connective tissue, synovial
fluid and vitreous humor of the eye.
 It serves as a lubricant in joint cavities.

42.  It contains repeating units of D-Iduronate-2
SO4 and D-glucosamine-6-SO4 in alph-1,4
linkages.
 It is present in liver, spleen, lungs and
monocytes.
 It activates antithrombin III and inhibits
blood clotting.

43.  It is present in ground substance of
connective tissues
 it is composed of (beta -1,4 Linkage) D-
glucuronic acid and beta-1,3 linkage N-acetyl
galactosamine SO4 repeating units.
 It is widely distributed in cartilage, bone,
tendons, cornea and skin.

44.  Dermatan sulfate(DS) : It contains repeating units
of L- iduronic acid and N acetyl galactosamine
SO4 in beta-1,3 linkages.
 It is found in skin, blood vessels and heart
values.
 Heparan sulfate(HS) : It contains repeating units
of D-glucuronic acid sulfate or Iduronic acid
sulfate and N-acetyl glucosamine sulfate.
 It has more amount of N-acetyl glucosamine
residues than heparin.
 It is present in the basement membrane of renal
glomerulus and cell surfaces.
 It helps in glomerular filtration and cell to cell
communications.

45.  Keratan Sulfate (KS): It is composed of
repeating units of D-galactose and N-acetyl
galactosamine sulfate. It does not contain
uronic acid. It is present in cornea and
tendons as a structural component.
 Glycoproteins and mucoproteins : If the
carbohydrate content is less than 10% , it is
called as glycoprotein and if carbohydrate
content is more than 10% ,it is called as
mucoprotein.

47.  In glycoproteins, protein component is
predominant
 The oligosaccharide chains are covalently
bound to proteins which may be either O-
linked or N-linked.
 Eg: Immunoglobulins, blood group
substances, Insulin receptor etc.
 They are also involved in cell to cell
recognition.

49.  Proteoglycans: They contain
glycosaminoglycans as a major component
with lesser protein.
 It occurs in extracellular matrix of connective
tissue , synovial fluid of joints, cartilage
,mucous secretion.
 Peptidoglycans: They are complex of
polysaccharides chains and polypeptides in
bacterial cell wall.
 Penicillin , an antibiotic inhibits the
peptidoglycan cross linking and kills the
bacteria.

51.  β , L- fucose is 6-deoxy β ,L - galactose.
 It is the fundamental subunit of the fucoidan
polysaccharide. α(1→3) linked to core .
 Fucose is a suspected carbohydrate antigen
for IgE-mediated allergy.
 L-Fucose is claimed to have application in
cosmetics, pharmaceuticals, and dietary
supplements.

53.  They are the indigestible portion of plant foods
that move food through the digestive system,
absorbing water and easing defecation.
 Insoluble fibers
 Make the feces bulk, softer and shorter the
transit time.
 Sources: Whole wheat, tomato peel, green beans
 Soluble fibers
 They are the edible carbohydrates resistant to
digestion and absorption in the human intestine
which undergoes complete or partial
fermentation in the large intestine .

54.  Sources: skin, pulp, seeds, stems leaves,
roots legumes, onion, carrots, potatoes, oats
etc.
 On fermentation, butyric acid is formed which
increases insulin release , decreases
cholesterol synthesis, Low density lipoprotein
and triglycerides levels, increases mineral
absorption and improves immunity.

56.  Adult : Fiber intake 20 – 35 gm/day . In
children, the requirement is = Children age in
years +5 gm/day

57.  A sugar substitute is a food additive that gives
the taste of sugar with less or no calories and
they may be natural or synthetic compounds.
 Those that are synthesized are called artificial
sweeteners which are chemicals that give the
sweetness of sugar with no or less calories and
usually are sweeter than sugar.
 Eg. Aspartame is heat unstable and is a methyl
ester of the aspartic acid/phenylalanine
dipeptide.
 Saccharin, sucralose (chlorinated sucrose),
sorbitol are also sugar substitutes.

58.  Mucopolysaccharidosis : They are inborn errors
characterized by accumulation
glycosaminoglycans (mucopolysaccharides) in
various tissues causing skeletal and extracellular
matrix deformities due to inherited enzyme
defects.
 In MPS disorders, Skeletal changes, mental
retardation, visceral involvement and corneal
clouding are manifested due to particular MPS
deposits and its excretion in urine.
 That can be detected in urine by Cetyl Trimethyl
Ammonim Bromide (CTAB) test or O-tolidine
blue test.

60.  Glycome and Glycomics
 Glycome is the total complement of all the
carbohydrates in an organism. Glycomics is
the study of structure and function of
glycome.

61.  Thank you